Environmental effect on mechanical properties of aluminide matrix composites

This paper investigates the validity of the toughness measurement with a va riation of the loading rate for distinguishing the fracture mechanism of al uminide intermetallics and their composites. The ductility and fracture tou ghness of Ni3Al alloys and their composites are governed by inherent grain boundary brittleness and moisture-induced embrittlement at ambient temperat ures. Although B doping is effective in suppressing both factors, remarkabl e improvement of toughness mainly depends on grain boundary strengthening. The toughness of the alloys is influenced by the dislocation locking mechan ism and the extrinsic embrittlement promoted by diffusion of oxygen at inte rmediate temperatures. Extrinsic embrittlement is the predominant mechanism in determining the toughness at 673 Ii. Restriction of the dislocation mot ion is the predominant factor in determining toughness at 873 and 1073 K. T he composites reinforced with TiC particles exhibit exceptionally constant toughness at 300 to 900 K.